Crystalline metaboric acid by hydrolysis of secondary alkyl borate ester



United States Patent 3,415,621 CRYSTALLINE METABORIC ACID BY HYDROLY- SIS OF SECONDARY ALKYL BORATE ESTER Peter W. Gilderson, Oakland, Stanley F. Newman, San

Francisco, and Lloyd C. Fetterly, Oakland, Calif., assignors to Shell Oil Company, New York, N.Y., a corporation of Delaware No Drawing. Filed Dec. 17, 1965, Ser. No. 514,716 3 Claims. (Cl. 23-449) ABSTRACT OF THE DISCLOSURE When aliphatic secondary alcohols are produced by the controlled oxidation of paraffins in the presence of oxyboron compounds, an improved continuous process is obtained by separately hydrolyzing the resulting secalkyl borate ester in a controlled manner with a limited proportion of water directly to the alcohol and predominantly metaboric acid (HOBO) in crystalline form, and recycling the crystalline metaboric acid to the oxidation zone.

This invention relates to the production of alcohols by the controlled oxidation of parafiins. More particularly, this invention is concerned with the continuous production of secondary alcohols by the controlled reaction of paraffins with an oxygen-containing gas in the presence of oxyboron compounds.

Oxidation of organic compounds with the aid of a variety of oxyboron compounds has been accomplished. The oxidation of aliphatic hydrocarbons to sec-alkyl borate esters with oxygen in the presence of boric oxide or boric acid is known (see, for example, T. Hellthaler et al., German Patent 552,886, Apr. 19, 1932). The borate esters can be hydrolyzed to yield corresponding secondary alcohols. Saturated hydrocarbons can also be converted to alcohols by reaction with oxygen and borate esters or esters of boronic and borinic acids (see, for example, Netherlands application 6409181, Feb. 22, 1965). Similarly oxidation in the presence of metaboric acid is known (see, for example, S.N. Fox et al., US. 3,109,864, Nov. 5, 1963). Copending US. application of L. C. Fetterly et al., Ser. No. 485,564, filed Sept. 7, 1965, demonstrates the conversion of parafiins to secondary alcohols by use of trialkoxyboroxines.

The commercial utility of any of these routes to produce secondary alcohols is determined to a great extent by the recovery and reuse of the oxyboron component from the resulting sec-alkyl borate esters. In the prior art processes, the borate esters are hydrolyzed to produce in the main orthoboric acid (H BO Although orthoboric acid can be reused directly, it is not an efficient compound for the controlled oxidation of paraffins and generally is converted by additional processing to a more preferred oxyboron component.

It is, therefore, a principal object of the present invention to provide an eflicient and improved process for the production of predominantly secondary alcohols by the controlled oxidation of paraflins in the presence of certain oxyboron compounds and hydrolyzing the resulting esters to produce directly more effective oxyboron compounds for reuse in the initial oxidation stage.

Now, in accordance with this invention, it has been found that, when aliphatic secondary alcohols are prepared by the controlled oxidation of paraffins in the presence of oxyboron compounds, an improved continuous process is obtained by separately hydrolyzing the resulting sec-alkyl borate ester in a controlled manner with a limited proportion of water directly to the alcohol and solid metaboric acid (HOBO), and recycling the metaboric acid to the oxidation zone.

3,415,621 Patented Dec. 10, 1968 The parafiins useful in the process of this invention are saturated aliphatic hydrocarbons of from 6 to 40 carbon atoms which can be normal or branched, and acyclic or cyclic, and essentially free of aromatics. Satisfactory results are obtained especially with paraflins designated RH, where R is an aliphatic hydrocarbyl of 8 to 30 carbons and preferably of 10 to 20 carbons, especially alkyl of 10 to 20 carbons. Representative examples of suitable hydrocarbons include n-hexane, cyclohexane, noctane, 2-ethylhexane, n-nonane, n-dodecane, n-tetradecane, eicosane, hexacosane, triacontane, and the like, including their mixtures.

The paraffin is oxidized in liquid phase with molecular oxygen, the controlled oxidation being carried out in the presence of an oxyboron compound, preferably metaboric acid or any dehydrated form of orthoboric acid. The source of molecular oxygen is any oxygen-containing gas as, for example, air or oxygen diluted to any desired extent with an inert gas such as nitrogen, methane, carbon dioxide, and the like.

The oxyboron compounds useful in the initial oxidation stage of the process are those of the prior art named hereinabove. Since the operation of the process according to the invention converts the oxyboron moiety to predominantly metaboric acid after the initial stage, and recycles the metaboric acid to the oxidation reactor, the subsequent operation of the process is essentially controlled oxidation of paraflin in the presence of metaboric acid. The advantage residing in the invention is the direct conversion of the oxyboron moiety to predominantly metaboric acid, avoiding the conventional twostep operation wherein the oxyboron moiety is converted to orthoboric acid followed by conversion of the orthoboric acid to an oxyboron compound more efiicient in the controlled oxidation of paraffins.

In general, it is desirable to provide at least one gram atom of boron in the form of oxyboron compound for each gram mole of paraffin being oxidized. However, greater or lesser amounts may be utilized if desired. A suitable range may include, for example, the use of about 0.3 to about 4.5 gram atoms of boron in the form of oxyboron compound per gram mole of paraffin being oxidized. A preferred range includes the use of about 0.6 to about 2.1 gram atoms of boron in the form of oxyboron compound per gram mole of parafiin being oxidized.

In addition, a polyvalent heavy metal compound catalyst which is soluble in the reaction mixture may optionally be employed in a catalytically effective amount. Thus, for example, soluble salts of cobalt, manganese, lead, iron, and the like, may be used in the form of acetate, octoate, stearate, and the like. Preferred compounds include those such as cobalt octoate, cobalt stearate, and the like. The amount of such additional reagent may be such that the reaction mixture contains from about 0.001 to 0.2% by weight (based on total weight of paraflin to be oxidized) of solu-bilized polyvalent heavy metal.

The controlled oxidation and concomitant esterification are conducted at a temperature Within the range of about to about 300 C. at a pressure sufficient to prevent excessive loss of parafiin with the exit gas. Pressures within the range of about 15 to about 1000 p.s.i.a. can be employed. A preferred temperature range is from about to about C.

At the completion of the controlled oxidation, unconverted paraflin and ketone by-product are removed from the mixture by any suitable means, for example, by vacuum flashing. The remaining product is a boron .ester complex of the initial oxyboron compound and a secondary alcohol, from which the desired secondary alcohol is recovered by subsequent hydrolysis. Conventional hydrolysis of the boron ester complex produces secondary alcohol and aqueous orthoboric acid. Optionally, with lower molecular weight parafiins, the unseparated parafiin and ester complex mixture resulting from the initial oxidation may be hydrolyzed. After hydrolysis and recovery of the oxyboron moiety, the remaining mixture of lower paraffin and secondary alcohol may then be separated.

According to the invention, controlled hydrolysis of the aforesaid ester complex produces secondary alcohol and predominantly meta boric acid in a solid form. This is accomplished by adding a limited proportion of water to the ester complex at a temperature in the range of 140 to 220 C., preferably from about 165 C. to 175 C. The water may be added as a liquid, as steam, or as a vapor diluted with an inert gas, for example, nitrogen. This appropriate amount of water hydrolyzes the ester complex to produce the secondary alcohol and predominantly metaboric acid in solid form. The ester complex comprises mainly sec-alkyl borate ester, which, in operating practice, has been found to contain a sec-alkylzboron molar ratio varying from 1:1 to 3: 1, but more often being about 1.521. These ratios clearly depend on the initial quantity of oxyboron compound used and the degree of conversion of initial parafiin. Consequently the limited quantity of water to be added is more appropriately determined from analysis of the sec-alkyl content and boron content of the ester complex. In accordance with the invention, hydrolysis of the ester complex with a molar amount of water approximately equal to onehalf the sum of the moles of sec-alkyl groups plus the moles of boron in the ester complex will produce secondary alcohol and solid metaboric acid. Another way of expressing the required proportion of water is in terms of moles of water per mole of boron:

moles Ego/mole B: (moles secal2kyl/mole B) +1 In practice the solid metaboric acid is produced in a finely divided state in the presence of the aforesaid control-led amount of water. The solid metaboric acid so produced is crystalline in form and is predominantly metaboric acid although there may be a minor proportion by weight of orthoboric acid or a dehydrated form of orthoboric acid contained therein.

Although treatment of the aforementioned ester complex with water produces immediate hydrolysis thereof, the addition of a small amount of acid or base as a hydrolysis catalyst does not adveresly affect the process. From a practical consideration, the controlled hydrolysis of the invention is carried out in the absence of any substantial amount of added base.

The production of metaboric acid in crystalline form lends itself to economic processing in that no excess water need be removed as in aqueous solutions of orthoboric acid. The products resulting from the controlled hydrolysis may then be resolved by any suitable method, for example, distillation, phase separation, fractional crystallization, or a combination thereof, in order to recover the desired secondary alcohol, and to recycle the metaboric acid. A preferred mode of operation encompasses separating the metaboric acid by centrifugation or filtration and returning the crystalline metaboric acid to the oxidation reactor, conveniently as a slurry in the paraffin to be oxidized. Continuous operation is thereby achieved by this novel process for regenerating the oxyboron compound as predominantly metaboric acid in crystalline form.

The secondary alcohol may require a water wash to remove residual oxyboron compound. The resulting aqueous solution containing oxyboron compound may optionally be used as hydrolysis water and returned to the controlled hydrolyser, thereby minimizing losses of boron compound. A multistage countercurrent hydrolysis would be even more effective. Optionally the secondary alcohol may be additionally purified by distillation, fractional crystallization, and the like. It may be hydrogenated to reduce any carbonyl and unsaturation content.

In order to improve over-all efficiency of the process, the separated mixture of unconverted parafiin and ketone by-product may be hydrogenated to convert the ketone to paraffin or alcohol and the resulting material recycled to the oxidation reactor. Alternatively the ketone may be removed by adsorption, for example, on alumina.

The following specific example of the invention will serve to illustrate more clearly the application of the invention, but the details thereof are not to be construed as limiting the invention.

EXAMPLE I n-Dodecane is contacted with 20% oleum at ambient temperature to remove aromatic components. Following the acid treatment, 2840 grams (16.7 moles) of ndodecane is charged to a stainless-steel oxidation reactor vessel containing 88 grams (2 moles) of metaboric acid. To the well-agitated reactor vessel, equipped with a reflux condenser, is passed a Ng/Og mixture containing 3.5% by volume of oxygen. The mixture is heated at 165 C. until 1.7 moles of oxygen is reacted with the ndodecane, and 20% conversion of the n-dodecane is obtained. Unreacted n-dodecane and by-product ketone are removed from the resulting boron esters of secondary C alcohol by flashing at about 171 C., in two stages, One at 25 mm. Hg and the other at 8 mm. Hg, yielding 661 grams of esters. Control analysis of esters indicated that they contained 2.0 moles of boron and 3.2 moles of sec-dodecyl groups resulting in a sec-C H :B ratio of 1.6:1. This product is then heated to 165 C. at 20 p.s.i.g. and 47 grams (2.6 moles) of water is slowly added with moderate stirring. After all the water is added, the mixture is cooled, centrifuged, .and the resulting crystalline metaboric acid grams) is slurried with fresh n-dodecane and recycled to the stainless-steel oxidation reactor vessel. The liquid phase from the centrifuge is given a water wash and redistilled to obtain 464 grams of sec-dodecyl alcohols.

We claim as our invention:

1. The process of producing predominantly metaboric acid in a crystalline form by hydrolyzing secondary alkyl borate ester with water in a molar amount equal to onehalf the sum of the moles of sec-alkyl groups plus the moles of boron in said ester at a temperature of to 220 C.

2. The process according to claim 1 wherein said temperature is to 175 C.

3. The process according to claim 1 wherein said secondary alkyl group is one of 6 to 40 carbon atoms.

References Cited UNITED STATES PATENTS 3,232,704 2/1966 Helbig et al. 3,275,695 9/1966 Marcell. 3,324,186 6/1967 Olenberg.

OTHER REFERENCES Bashkirov et al.: World Petr. Congress, 5th Proceedings, New York, 1959, vol. 4, pp. 175-83.

LEON ZITVER, Primary Examiner.

I. E. EVANS, Assistant Examiner. 

